Timing devices



July 25, 1961 D. L. MORGAN TIMING DEVICES Filed June 27, 1957 Fig. I

34v 42 "7 22 20 I8 36 f? ,21

Fig.

TEMPERATURE C IN VEN TOR.

DAVID L. MORGAN ATYUKA [Y United States Patent 2,993,965 TIMING DEVICESDavid L. Morgan, Shelton, Conn., assignor to Robertslraw-Fulton ControlsCompany, Richmond, Va., a corporation of Delaware Filed June 27, 1957,Ser. No. 668,390 2 Claims. (Cl. 20034) This invention relates to timingdevices and more particularly to hydraulic timing devices which arecompensated for changes in viscosity of the fluid caused by changes oftemperature.

In the usual form of hydraulic timing devices, a fluid is forced from anexpansible chamber through a capillary tube to a reservoir by applyingpressure to the expansible chamber. Accordingly, a time delay isestablished corresponding to the time required to displace the fluidfrom the expansible chamber to the reservoir.

Such devices are subject to an inherent disadvantage in that theviscosity of the fluid changes with the temperature thereof. It will beapparent that if the viscosity of the fluid changes, the rate of flow ofthe fluid from the expansible chamber will also vary, causing variationsin the time delay.

It is an object of this invention to utilize a fluid to produce a timedelay substantially unaffected by temperature variations of the fluid.

Another object of this invention is to compensate a hydraulic timingdevice for variations in viscosity of the fluid.

In the preferred embodiment of the invention, a pair of expansibleelements are connected by a capillary tube and filled with a suitablefluid. Means are provided for biasing one of said elements to acontracted condition, and means are provided for actuating the other ofsaid elements to force the fluid therein into the one element to expandthe same against its bias to thus establish a time delay determined bythe time required for the fluid to return to said other element underthe force of said biasing means. A volume of fluid is used so that achange in viscosity of the fluid as a result of a temperature change iscompensated for by the thermal expansion of the fluid in response to thetemperature change.

Other objects and advantages will become apparent from the followingdescription taken in connection with the accompanying drawing wherein:

FIG. 1 is a longitudinal sectional view in somewhat schematic form of acontrol device embodying this invention; and

FIG. 2 is a graph illustrating the operation and result achieved by theinvention.

Referring more particularly to the drawing, the timing device comprisesa casing having mounted therein a pair of spaced parallel expansible andcontractible bellows member 12, 14. The bellows member 12 defines anexpansible chamber 13 and has one end sealed to a plate 16 fixed to'thebottom wall of the casing 10 and its other upper end sealed to a disc18. An actuating plunger 20 extends from the disc 18 and is slidablymounted in a suitable opening 22 in the upper wall of the casing 10, inaxial alignment with the bellows member 12. A flange 24 is formed on theupper end of the plunger 20 to enable the plunger 20 to be manuallyactuated axially toward the bellows member12. The plunger 20 provides ameans for manually contracting the bellows member 12. It will beapparent that if the plunger 20 is manually depressed, the upper end ofthe bellows member 12 will be moved axially toward the bottom wall ofthe casing 10 to reduce the volume of the chamber 13.

The other bellows member 14 defines an expansible chamber 25 and has oneend sealed to a suitable plate 26 fixed to the bottom wall of the casing10 and the other end thereof sealed to a disc 27 engaging the bottomwall of a cup-shaped member 28, the member 28 substantially enclosingthe bellows member 14. The lower end of the cup-shaped member 28terminates in a flange 30 providing a seat for a spring 32 mounted incompression between the flange 30 and the upper wall of the casing 10.The spring 32 serves to bias the bellows member 14 downward tending tocontract the same to decrease the volume of the chamber 25.

An actuating stem 34 extends upwardly from the end wall of thecup-shaped member 28 and is slidably mounted in a suitable opening 36formed in the upper wall of the casing 10. The upper portion of theactuating stem 34 is reversely bent at 38 and carries an electricalcontact 40 on the end thereof for cooperation with a fixed contact 42fixed to an abutment on the exterior surface of the upper wall of thecasing 10. The contacts 40, 42 may be connected by suitable lead wires(not shown) to an electrical device (not shown) to be controlled.

In the position shown in FIG. 1, the contact 40 is out of engagementwith the contact 42. However, the contact 40 will move into engagementwith the contact 42 upon downward axial movement of the actuating stem34 during contraction of the bellows member 14 under the bias of spring32 to engage the contact 42.

The chamber 25 of the bellows member 14 communicates with the chamber 13of the bellows member 12 by means of a capillary tube 44 which has theends thereof sealed within the bottom wall of the casing 10 incommunication with the chambers 13, 25, respectively. The capillary tube44 is reduced in diameter at 46, preferably at its medial portion, todefine a restricted flow passage 48. The bellows members 12, 14 andcapillary tube 44 define a closed system filled with a viscous fluid,such as heptane. In addition, the bellows members 12, 14 and capillarytube 44 operate in conjunction with the parts described in connectiontherewith to form a hydraulic timing device, the operation of which maybe described as follows.

In operation of the timing device, the plunger 20 is manually depressedto the position shown in FIG. 1. This movement of the plunger 20 willserve to compress the bellows member 12 and force fluid from the chamber13 through the capillary tube 44, passage 48 and into the chamber 25 ofthe bellows member 14. This forcing of fluid into the bellows member 14causes expansion of the same against the bias of the spring 32and-movement of the actuating stem upward to the position shown, e.g.,wherein the contact 40 is disengaged from the contact 42 The sequence ofoperation discussed thus far will condition the timing device to effecta delayed closing of contacts 40, 42. More particularly, when theplunger 20 is released in its depressed position illustrated in FIG. 1,the bellows member 14 will contract under the bias of the spring 32 toundergo reduction in volume and force fluid from the chamber 25 throughthe capillary tube 44 to the bellows member 12. The rate of contractionof the bellows member 14 is determined by the biasing force of thespring 32, the volume of the bellows member 14, the size of restrictedpassage 48, and the viscosity of the fluid filling the system.

After a predetermined time delay which is determined by the foregoingfactors, the bellows member 14 will have contracted sufficiently tocause engagement of the contact 40 with the contact 42 and to havereturned the plunger 20 to its uppermost position. Normally, atemperature change causing a change in viscosity of the fluid fillingthe bellows members 12, 14, and capillary tube 44 would vary the timedelay established as above described since, as the fluid becomes moreviscous, the flow rate thereof through the orifice 48 will decrease.

However, the physical variables in the device have been so selected soas to compensate for any change in viscosity of the fluid as the resultof a change in temperature of the fluid. More particularly, it has beenfound that by accurately selecting the volume of the fluid, a change inviscosity can be offset or balanced by a change due to thermal expansionof the fluid as a result of the temperature increase.

Referring to FIG. 1, it will be apparent that when the plunger 20 isdepressed to the position shown, the spacing between the two contacts40, 42 willvary with the temperature of [the fluid due to the thermalexpansion of the fluid in response to a temperature increase. Thisvariation in volume of the fluid with temperature will depend on thetotal volume of the fluid and the thermal coeflicient of expansion ofthe fluid. Thus, it will be apparent that at a predeterminedtemperature, a portion of the fluid sufiicient to expand the bellowsmember 14 to open the contacts 40, 42 and having a predeterminedviscosity will flow through the orifice or passage 48 in a time whichmay be determined from the following equation:

where t is time delay at temperature T v is volume of fluid flowingthrough the orifice at temperature T n is the viscosity at temperatureT;

K is a constant for varying temperature.

Assuming now a temperature increase of the fluid to a temperature T thefollowing equation may be written:

where the new terms are:

t is time delay at temperature T V is the total volume of fluid in thesystem at T n is the viscosity at temperature T a is the thermalcoeflicient of expansion of the liquid.

If the ratio of t to t is determined, the following equation results:

When the ratio of t to t is unity, the last equation becomes:

From this last equation, it will be apparent that the time delay at twodifferent temperatures can be made substantially constant by a properchoice of For purposes of illustration, assume that it is desired thatthe time delays t and t be equal at temperature of 50 C. and +50 C. whenthe liquid is heptane. The following tabulation gives the necessaryvalues:

n 1.177 .3128 density .7420 .6583

From the above density data (a may be calculated as a n as tfl m R TmFor heptane AE=1897 calories and R=l.987 calories. It is evident thatsince viscosity is an exponential function of T and volume is almost alinear function of T that the ratio can be exactly unity at only twogiven values of T for a certain ratio of Referring to the graphillustrated in FIG. 2, the ratio of t to t, for heptane is plottedbetween the temperature of 75 C. and C. From the graph it can be seenthat with heptane, the range of 58 C. to +100 C. results in not morethan i-l0% variation in time delay.

From the foregoing it will be apparent that by properly selecting thevolume of the liquid filling the bellows members '12, 14 and tube 44 asillustrated for the above equations, a time delay is obtained which issubstantial- 1y constant during normal variations in temperature of thefluid used.

While only one embodiment of the invention has been shown and describedherein, it will be apparent that many modifications and changes may bemade without departing from the scope of the invention as defined in theappended claims.

I claim:

1. In a fluid actuated constant delay timing device exposed to avariable ambient temperature, the combination comprising a supportmeans, first and second hollow expansible and contractible elementssecured to said support means and being spaced adjacent to each other, acapillary tube connected to each of said first and second elements andbeing adapted to communicate with the hollow interiors of said first andsecond elements, said hollow interiors of said first and second elementsand said capillary tube forming a chamber of a predetermined volume andproportional to the volume of liquid flow through said capillary tubefor a given ambient temperature range, a viscous fluid filling saidfluid chamber, a positive displacement actuating meansoperativelyconnected to said second element for displacing apredetermined amount of fluid, biasing means adapted for exerting asubstantially constant contracting force on said first element, saidbiasing means being responsive to the release of said actuating means tocause the return of said predetermined amount of fluid from the hollowinterior of said first element to the hollow interior of said secondelement via said capillary tube, and contact means operativelyassociated with said first element for controlling an electricalcircuit, said fluid being adapted to expand and contract said firstelement in response to different temperature ambients to variably adjustsaid contact means, the viscosity of said fluid varying in response tovariable ambient temperatures whereby said first element compensates forchanges in total volume and viscosity of said fluid upon changes in saidambient temperature to obtain uniform time response to adjust saidcontact means when said actuating means is released.

2. A timing device as Claimed in claim 1 wherein said first and secondelements and said capillary tube are constructed in accordance with theequation v is the volume of fluid flowing through said capillary 10 tubeupon release of said fluid at T n is the viscosity of fluid at T and ais the thermal coefiicient of expansion of said fluid.

References Cited in the file of this patent UNITED STATES PATENTSYoungman May 6, 1884 Kellett June 27, 1933 Turner Apr. 27, 1948 Davisonet a1 May 5, 1953 Troendle May 5, 1953 OTHER REFERENCES Germany Jan. 28,1927

